The new season will presumably take place after the events of Frozen, with Elsa escaping from the urn in which she was kept in the Season 3 finale.

Horowitz said, "What happened to her to get her into that urn and what was going on in her life at that point is what's going to be revealed and what's going to be pushing the story forward."

"Hopefully you'll find that there will be some cool surprising connections between Arendelle and our world," he added.

Elsa and Anna's parents were only featured at the beginning of Disney's Frozen, but they will likely be explored further in ABC's Once Upon a Time this season.

Meanwhile, Horowitz recently told The Hollywood Reporter that they were "honoured" to be able to incorporate the Frozen universe and characters into the hit series.

"We fell in love with [the movie] when it came out last year like everyone did, and we want to do our best to do it justice," he said.

Once Upon a Time is heavily banking on hit animated movie Frozen in Season 4, with the inclusion of Elsa (Georgina Haig), Anna (Elizabeth Lail), Kristoff (Scott Michael Foster), Hans (Tyler Jacob Moore) and elder troll Pabbie (voiced by John Rhys-Davies).